Antifriction bearing and the use thereof in an nmr tomograph

ABSTRACT

The invention relates to an antifriction bearing (W 2 ) for an NMR tomograph (KT) having magnetic rolling members ( 23 ), and having an inner ring ( 21 ) and an outer ring ( 22 ) between which the rolling members ( 23 ) roll along, the outer ring ( 22 ) being surrounded by a nonmagnetic ring ( 24 ). The invention also relates to the use of a magnetic antifriction bearing (W 2 ) for an NMR tomograph (KT).

[0001] The invention relates to an antifriction bearing for an NMR tomograph and its use for an NMR tomograph.

[0002] Many components of an NMR tomograph should be as nonmagnetic as possible so that a magnetic field produced for an examination by NMR tomography is not overlaid by an additional magnetic field. Consequently, as regards the guiding rollers of a patient couch of the NMR tomograph use is made of nonmagnetic antifriction bearings whose rolling members are produced from ceramic and whose inner and outer rings, between which the rolling members roll along, are produced from nonmagnetic and hardened steel. However, such antifriction bearings are expensive to produce. Nonmagnetic antifriction bearings suitable for NMR tomographs are produced, for example, by INA Walzlager Schaeffler KG, as may be gathered from their technical product information TPI 41, published in April 1995.

[0003] For example, guiding rollers for conveying engineering are divulged on page 40 of the main catalog 94/96 of the Rader-Vogel wheel and roller factory, Sperlsdeicher Weg 19-23, 21109 Hamburg. The guiding rollers are fabricated from a special material and surrounded by a special ballbearing.

[0004] Moreover, a guiding roller on vehicle doors is disclosed in DE 1 892 000 U. A ballbearing is pressed in in the guiding roller consisting of plastic.

[0005] It is therefore the object of the invention to design an antifriction bearing for an NMR tomograph in such a way as to reduce the fabrication costs for the latter.

[0006] According to the invention, this object is achieved by means of an antifriction bearing for an NMR tomograph having magnetic rolling members, and having an inner ring and an outer ring between which the rolling members roll along, the outer ring being surrounded by a nonmagnetic ring. Thus, use is made as rolling members of conventional magnetic rolling members that can be produced in large batch numbers and thus cost-effectively.

[0007] In accordance with variants of the invention, the nonmagnetic ring can have nonmagnetic steel, nonmagnetic brass and/or nonmagnetic copper.

[0008] In order to keep low the costs of fabrication in the production of an antifriction bearing according to the invention, it is provided in one design of the invention that the outer ring is pressed into the nonmagnetic ring.

[0009] The costs of fabrication can be further lowered if, according to a further variant of the invention, the inner ring and/or the outer ring are magnetic. Magnetic antifriction bearings with magnetic and hardened rolling members, and inner and outer rings can, moreover, be designed to be substantially smaller than nonmagnetic antifriction bearings with ceramic rolling members whilst maintaining the same load rating. Thus, in accordance with a particularly preferred embodiment of the invention, the outside diameter of the nonmagnetic ring can be designed to be at least 1.5 times larger than the outside diameter of the outer ring. Consequently, the spatial extent of the magnetic components of the antifriction bearing according to the invention is small, and the magnetic field produced by the magnetic components then, if at all, have scarcely any disturbing effect on the mode of operation of the NMR tomograph.

[0010] Further variants of the invention provide that the antifriction bearing is a ballbearing or a double-row ballbearing.

[0011] One embodiment of the invention provides that the rolling members are spherical and have a diameter of between 3 mm and 8 mm, and that the nonmagnetic ring has an outside diameter of between 55 mm and 65 mm.

[0012] The object is also achieved by means of the use of an antifriction bearing having magnetic rolling members for an NMR tomograph. Such an antifriction bearing can be produced more cost-effectively than a nonmagnetic antifriction bearing, the result being to reduce the production costs of the NMR tomograph.

[0013] Further advantages follow from the subclaims.

[0014] Exemplary embodiments of the invention are illustrated in the attached schematic drawings, in which:

[0015]FIG. 1 shows a conventional nonmagnetic antifriction bearing,

[0016]FIG. 2 shows an antifriction bearing according to the invention, and

[0017]FIG. 3 shows an NMR tomograph having an antifriction bearing according to the invention.

[0018]FIG. 1 shows a schematic sectional view of a conventional magnetic antifriction bearing W₁ for an NMR tomograph. The antifriction bearing W₁ shown in FIG. 1 is designed as a ballbearing.

[0019] The antifriction bearing W₁ has an inner ring 1 and an outer ring 2 that are produced, for example, from nonmagnetic and hardened steel. Spherical rolling members 3 that can roll along between the inner ring 1 and the outer ring 2 are arranged between the inner ring 1 and the outer ring 2. The spherical rolling members 3 are fabricated from ceramic, for example, and are therefore nonmagnetic.

[0020] The antifriction bearing W₁ illustrated in FIG. 1 is provided for supporting a patient couch 30, illustrated in FIG. 3, of an NMR tomograph KT. In order to achieve a load rating of the antifriction bearing W₁ that is suitable for the use of the antifriction bearing W₁ illustrated in FIG. 1, the spherical rolling members 3 are relatively large, and this has a negative effect, inter alia, on the production costs of the antifriction bearing W₁.

[0021]FIG. 2 shows a sectional view of an antifriction bearing W₂ according to the invention for an NMR tomograph. The friction bearing W₂ shown in FIG. 2 is a double-row ballbearing in the case of the present exemplary embodiment. The friction bearing W₂ according to the invention has an inner ring 21 and an outer ring 22 between which spherical rolling members 23 can roll along. The inner ring 21, the outer ring 22 and the rolling members 23 are fabricated in the case of the present exemplary embodiment from a magnetic and hardened steel. Moreover, the outer ring 22 of the antifriction bearing W₂ is pressed into a nonmagnetic ring 24 which is fabricated in the case of the present exemplary embodiment from a nonmagnetic steel.

[0022] The antifriction bearing W₂ illustrated in FIG. 2 is provided for installation in an NMR tomograph KT instead of the antifriction bearing W₁ shown in FIG. 1. Consequently, the inner rings 1 and 21 of the antifriction bearings W₁ and W₂ shown in FIGS. 1 and 2 have at least substantially the same inside diameter d₂ and d₂₁, respectively, in the case of the present exemplary embodiment. Moreover, the nonmagnetic ring 24 of the antifriction bearing W₂ illustrated in FIG. 2 has an outside diameter D₂₄ that is at least substantially equal to the outside diameter D₂ of the outer ring 2, illustrated in FIG. 1, of the antifriction bearing W₁. In the case of the present exemplary embodiment, the outside diameter D₂ of the outer ring 2 and the outside diameter D₂₄ of the nonmagnetic ring 24 are 62 mm.

[0023] Magnetic antifriction bearings with magnetic and hardened rolling members, and inner and outer rings have a higher load rating than do nonmagnetic antifriction bearings with ceramic rolling members. The spherical rolling members 23 of the antifriction bearing W₂ according to the invention can therefore be designed to be substantially smaller than the nonmagnetic spherical rolling members 3 of the conventional nonmagnetic antifriction bearing W₁ shown in FIG. 1. In the case of the present exemplary embodiments, the spherical antifriction bearing 3 of the nonmagnetic antifriction bearing W₁ has a diameter of 12 mm, the spherical magnetic antifriction bearings 23 of the antifriction bearing W₂ according to the invention only having a diameter of 5 mm.

[0024] Moreover, in the case of the present exemplary embodiment it is provided that the outside diameter D₂₄ of the nonmagnetic ring 24 is twice as large as the outside diameter D₂₂ of the outer ring 22 of the antifriction bearing W₂ shown in FIG. 2. Consequently, the magnetic components of the antifriction bearing W₂ shown in FIG. 2 have only a relatively small spatial extent, and so, by contrast with the magnetic field that is produced by an NMR tomograph for an examination, the magnetic field produced by the magnetic components of the antifriction bearing W₂ is small and therefore has an effect which, if [lacuna], scarcely disturbs the operation of the NMR tomograph.

[0025]FIG. 3 shows a rough schematic of an NMR tomograph KT for which the antifriction bearing W₂ according to the invention and shown in FIG. 2 is used. In the case of the present exemplary embodiment, it is provided to use the antifriction bearing W₂ shown in FIG. 2 for the purpose, in particular, of supporting a patient couch 30 of the NMR tomograph KT. However, other purposes are conceivable for the use of an NMR tomograph.

[0026] Moreover, the inner ring 21 and the outer ring 22 of the antifriction bearing W₂ illustrated in FIG. 2 need not necessarily be magnetic. Nonmagnetic inner rings 21 and/or outer rings 22 are also possible.

[0027] The spherical antifriction bearings 23 need not necessarily be produced from magnetic and hardened steel. They can also be produced from other magnetic materials.

[0028] The nonmagnetic ring 24 can also comprise materials having steel other than nonmagnetic steel as long as these materials are nonmagnetic. In particular, it is also possible to use nonmagnetic brass and/or nonmagnetic copper.

[0029] The antifriction bearing W₂ according to the invention need not necessarily be a double-row ballbearing. Other ballbearings or antifriction bearings having nonspherical rolling members, for example cylindrical rollers, needles, cones or barrels are also possible.

[0030] The abovenamed dimensions of the antifriction bearing W₂ according to the invention, and the size ratio between the outside diameter D₂₄ of the nonmagnetic ring 24 and the outside diameter D₂₂ of the outer ring 22 are likewise to be understood merely as being exemplary. 

1. An antifriction bearing for an NMR tomograph, having magnetic rolling members (23), and having an inner ring (21) and an outer ring (22) between which [lacuna] rolling members (23) roll along, the outer ring (22) being surrounded by a nonmagnetic ring (24).
 2. The antifriction bearing as claimed in claim 1, in which the nonmagnetic ring (24) has nonmagnetic steel, nonmagnetic brass and/or nonmagnetic copper.
 3. The antifriction bearing as claimed in claim 1 or 2, in which the outer ring (22) is pressed into the nonmagnetic ring (24).
 4. The antifriction bearing as claimed in one of claims 1 to 3, in which the inner ring (21) and/or the outer ring (22) are magnetic.
 5. The antifriction bearing as claimed in one of claims 1 to 4, in which the outside diameter (D₂₄) of the nonmagnetic ring (24) is at least 1.5 times larger than the outside diameter (D₂₂) of the outer ring (22).
 6. The antifriction bearing as claimed in one of claims 1 to 5, which is a ballbearing.
 7. The antifriction bearing as claimed in one of claims 1 to 6, which is a double-row ballbearing.
 8. The antifriction bearing as claimed in one of claims 1 to 7, in which the rolling members (23) are spherical and have a diameter of between 3 mm and 8 mm, and the nonmagnetic ring (24) has an outside diameter (D₂₄) of between 55 mm and 65 mm.
 9. The use of an antifriction bearing for an NMR tomograph (KT), in which the antifriction bearing (W₂) has magnetic rolling members (23).
 10. The use as claimed in claim 9, in which the magnetic rolling members (23) of the antifriction bearing (W₂) roll along between an inner ring (21) and an outer ring (22), and the outer ring (22) is surrounded by a nonmagnetic ring (24).
 11. The use as claimed in claim 9 or 10, in which the nonmagnetic ring (24) has nonmagnetic steel, nonmagnetic brass and/or nonmagnetic copper.
 12. The use as claimed in one of claims 9 to 11, in which the outer ring (22) is pressed into the nonmagnetic ring (24).
 13. The use as claimed in one of claims 9 to 12, in which the inner ring (21) and/or the outer ring (22) are magnetic.
 14. The use as claimed in one of claims 9 to 13, in which the outside diameter (D₂₄) of the nonmagnetic ring (24) is at least 1.5 times larger than the outside diameter (D₂₂) of the outer ring (22).
 15. The use as claimed in one of claims 9 to 14, in which the antifriction bearing is a ballbearing (W₂).
 16. The use as claimed in one of claims 9 to 15, in which the antifriction bearing is a double-row ballbearing (W₂).
 17. The use as claimed in one of claims 10 to 16, in which the rolling members (23) are spherical and have a diameter of between 3 mm and 8 mm, and the nonmagnetic ring (24) has an outside diameter (D₂₄) of between 55 mm and 65 mm. 